2989
through a square-root function, and the small positive deviation at higher temperatures is thought to be real. The fact that the magnetic moments reported for the europium complex are slightly below that expected for a J = 5/2 system may be a consequence of a slight shift in the g value. Such a shift has been noted for the 4f7 Gd3+ ion in metallic gadolinium and attributed to an interaction of the core electrons with the conduction band electrons. l 1 Further studies of the magnetic susceptibility and electron spin resonance of these and similar complexes are in progress. (11) M. Peter, etal., Phys. Rev., 126, 1395 (1962).
selected this relatively unique case to study how radiationless processes are affected by deuteration, both internally and externally. Tables I and I1 present our findings on the luminescence of CH3COCOCH3 (1-H) and CD3COCOCD3 (1-D) under various conditions. The measured lifetimes agree with those in the literature, being higher than those previously reported for 1-H at 77 OK and approaching the highest values reported in fluid solution.I4 We thus feel that adventitious quenchers are not playing a significant role in our measurements. Table I. Deuterium Enhancement at 77"Ke Biacetyl concn, M
Gerald R. Feistel, Thottakara P. Mathai Department of Chemistry, Saint Louis Uniuersity S t . Louis, Missouri 63156 Receiued March 11, 1968
0.10 0.05 0.01
0.005 0.05gb 0 .O W
Enhancement of Biacetyl Luminescence by Deuteration1i2
Sir: The mechanism of radiationless transitions between electronic states has been the subject of considerable theoretical and experimental4 study. Since nonradiative, rather than radiative, transitions are lifetime determining for many molecules of photochemical i n t e r e ~ t , ~ knowledge regarding the detailed nature of how one electronic state passes radiationlessly to another electronic state is crucial for the proper understanding of photochemical efficiencies. Available theories emphasize either the intramolecular3a-c or the i n t e r m o l e c ~ l a reffects ~~ which determine the rates of radiationless conversions. It is theoretially^"-^" expected, and experimentally found, 4,6 that the substitution of deuterium for hydrogen lowers the rate constant for radiationless transitions substantially, but has only a minor effect on radiative rates.7 However, this effect has not been observed in the condensed phases for any molecules if the states undergoing radiative interconversion are similar in energyn7 Essentially all of the data published to date pertains to the effect of deuterium substitution on organic molecules in rigid media.7 Since biacetyl emits both fluorescence8 and phosphorescenceg even in fluid solution, we have (1) Molecular Photochemistry. VII; paper VI: N. J. Turro and D. S. Weiss,J. A m . Chem. Soc., 90, 2185 (1968). (2) The authors gratefully acknowledge the generous support of this work by the Air Force Office of Scientific Research (Grants AFOSR1000-66 and AFOSR-1381-68), and the National Science Foundation (Grant NSF-GP-4280). We also thank Mr. C. I
